Field of the Invention
The present invention relates to a sheet conveying apparatus for conveying a sheet by a conveying belt having a suction hole while sucking the sheet.
Description of the Related Art
One example of a unit for conveying a sheet-type print medium, used in combination with an image printing apparatus, is a loop conveying belt that moves around while holding the print medium. With a conveying unit using the conveying belt, the print medium needs to be held without being displaced on the moving conveying belt. As the unit for holding the print medium on the conveying belt, a conveying unit using a suction system is known which adsorbs the print medium on the conveying belt by sucking air from a plurality of suction holes formed on the conveying belt. The suction system has advantages that the print medium can be held on the conveying belt and that small ink droplets (ink mist) not contributing to printing that are generated in the printing apparatus can be sucked and collected with air.
In general, in image printing apparatuses, small ink droplets are occasionally ejected together with main droplets when ink is ejected from ejection ports of a print head, and small ink droplets are occasionally generated by an impact or the like when ink droplets land on a print medium. These small ink droplets are sucked from the suction holes of the conveying belt as described above, but when the print medium comes near the suction holes, the ink droplets occasionally adhere to the print medium by going into an end portion or a back surface of the print medium, causing poor image quality. The adhesion of ink droplets causing such poor image quality is hereinafter referred to as an end portion stain or a back stain. In addition, an air flow toward suction holes occasionally causes displacement in the landing position of the main ink droplets ejected near the end portion of the print medium, which causes the image quality to fall out, leading to poor image quality.
On the other hand, US Patent Laid-Open No. 2002/0018097 discloses, as a technique of preventing the end portion stain, the back stain, and the landing displacement, an image printing apparatus in which a suction hole is formed only on two predetermined areas of a conveying belt and a print medium is fed to the conveying belt so as to cover one of the areas. According to the technique, there is no suction hole that is exposed to the outside near an end portion of the print medium, and therefore generation of an air flow causing the end portion stain, the back stain, and the landing displacement can be suppressed.
In US Patent Laid-Open No. 2002/0018097, however, the suction hole is provided only on the limited area on the conveying belt. Therefore, when a printing operation of a first sheet (first print) is started, the print medium and the suction hole may not be in an appropriate positional relation.
In this case, to match the position of the print medium with the position of the suction hole, it is required to have an operation of adjusting the positional relation between the area in which the suction hole is formed and the print medium by moving around the conveying belt before feeding the print medium to the conveying belt. This increases the time required before the first print.